The present invention relates to a magnetic brush device for developing electrostatic charge images on a photoconductive recording coating. In such a device, a developer consisting of a toner and of magnetic carrier particles is applied to the charge images, and the toner adheres to the charge images. The device has a doctor blade which bears against the magnetic brush roller, meters the quantity of carrier particles introduced by the magnetic brush roller for development and, at the ends of the roller, approaches the face of the roller.
A developing device of this general type is disclosed in German Offenlegungsschrift No. 2,436,890, wherein the carrier particles of the developer, after the end of the developing step, are removed from the photoconductive or dielectric recording coating by the action of magnetic forces. For this purpose, a magnet which, for example, is designed as a magnetic roller, is arranged at a small distance from the recording coating carrying the charge images. The distance between the magnet and the recording coating must, therefore, be such that the carrier particles cannot be jammed between the coating and the magnet.
German Offenlegungsschrift No. 2,162,842 describes a cascade developing device for an electrostatic copying apparatus which has a collecting device for removing the carrier particles adhering to the surface of the photoconductor drum. The collecting device consists of a sealing strip which does not touch the photoconductor drum and is formed from thin elastic material, for example, plastic, and which has a collecting edge. The collecting edge of the sealing strip is arranged at an adjustable distance from the carrier drum, which distance corresponds to about one tenth up to about half the diameter of the carrier particles. Neither wiping devices additional to the sealing strip nor a magnetic roller are provided.
U.S. Pat. No. 3,884,571 relates to a developing device having device for the developer extending in the shape of a trough in the axial direction along a drum immediately below the space between a developing station and the photoconductive recording surface of the drum. The base area of the trough comprises an upwardly-pointing, angled wiping lip which is located close to the surface of the drum and collects the developer which trickles down from the developing station. The developer collected in the trough is conveyed to an outlet opening with the aid of an endless revolving belt. Removal of the developer from the photoconductive recording coating by means of the magnetic roller is not envisaged.
In the case of developing devices which use a magnetic roller for applying the developer to the photoconductive recording coating and employ a doctor blade for wiping the developer from the surface of the magnetic roller, an increased discharge of carrier particles on the photoconductive recording coating is found in the region of the doctor transition, that is to say, the doctor zone close to the end faces of the magnetic roller, as compared with the center of the doctor blade. This makes it necessary to design the collectors so that they take up varying amounts of developer over the length of the doctor blade, as a result of which the manufacturing costs are increased.